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New audio system promises louder smartphone speakers

Perhaps not needed by the likes of Nokia's N8 and 808, but boding well for the rest of the mobile industry, a new audio system from NXP Semiconductors is set to boost the output power of micro speakers by over 5 times, "vastly improving the sound quality of mobile devices". Essentially, the new NXP TFA9887 chip will give mobile phones, portable music players and tablets louder and richer sound without risking speaker damage. It seems to work by massaging the audio signal to get more out of the speaker and can be compared to traditional sound compression techniques - the claim is that up to five times the 'music power' can be produced.

With a unique combination of safety features including adaptive excursion control and real-time temperature protection, the TFA9887 monitors speakers through a current-sensing amplifier and enables safe operation while working at near peak output at all times.

Speaker makers have to balance competing demands for good sound, small size and reliability. As micro speakers have shrunk, phone, media player and tablet designers have been forced to limit output power and sound quality. Amplifiers could easily deliver enough power to destroy the speaker at one frequency, while under-powering it at others. Until now, it has been impossible for system designers to know for sure when it was safe to apply extra power. The rule has therefore been to cut out bass frequencies and limit output power to avoid blowing the speaker – a common cause of failures in mobiles.

By incorporating circuits that monitor speaker performance and prevent damage, the NXP TFA9887 IC allows designers to break this rule. Adaptive excursion control measures the actual excursion of the speaker membrane to ensure that it never exceeds its rated limit. Real-time temperature protection measures the voice-coil temperature directly to prevent thermal damage.

Boosting audio performance

Because the speaker is fully protected, the system can deliver significant levels of extra power to make the sound louder and better than before. The TFA9887 optimizes the audio signal based on the movement of the speaker, something no other system is capable of, using the full capabilities of the speaker without pushing beyond the limits. An advanced clip avoidance algorithm monitors audio performance and prevents clipping, even when the power supply begins to sag. Bandwidth extension increases the low frequency response well below speaker resonance. And an intelligent DC-to-DC boost converter maximizes audio headroom from any supply level despite battery undervoltage. The TFA9887 automatically adapts to any changes in the speaker – including ageing, damage to the enclosure, and blocked speaker ports – helping to optimize performance and maintain the desired sound quality.

The entire system is integrated into a single chip with digital interfaces for portable devices. The IC incorporates NXP’s CoolFlux audio DSP, a high-efficiency class-D amplifier with current sensing, and a DC-to-DC boost converter. The advanced, embedded algorithms require no separate licensing. Additional tools allow designers to customize audio sound quality and choose how to optimize mobile device performance.

Impressive claims, though the proof will be in the devices, eventually - adapting to speaker ageing, damage, etc. seems like science fiction. Plus I'm sceptical how the waveform processing will improve most commercial music (and the better podcasts), which are already heavily compressed and optimised. Worth watching out for though!